The present invention relates generally to electrical terminals for removable attachment thereto of conductive elements and more particularly to a terminal used with printed circuit boards for receiving and removably retaining conductors or other circuit elements terminated in spade connectors having male prongs.
Use of twin pronged spade connectors is old technology not only in electronics manufacturing but also in many non-electronic electrical wiring applications. Flat headed machine screws threaded into a non-conductive strip provided an intermediate holding position where many connectors were brought when permanent and direct connections of elements was undesirable or as a distribution point where one element is required to connect to a plurality of other elements. The spade connector is slipped beneath the screw head with prongs straddling the screw body; the prongs are held against the terminal strip when the screw is tightened. The screws are isolated electrically one from the other or are joined by conductive strips as needed for the associated circuit, all in the known manner. The terminal strip using screw tightening permits simple disconnection of any individual conductor without need to unsolder or otherwise modify the existing wiring. A disadvantage in prior art terminal strips is the need to loosen and tighten the screws in order to fasten or remove a connector.
With the increasing use of printed circuit boards, the need became apparent for terminals which can be automatically attached to the circuit board, and can receive and hold spade connectors without screw fastening. U.S. Pat. No. 3,910,671 discloses a spade connector terminal designed for use with printed circuit boards and automatic board assembly techniques. The terminal is capable of automatically or manually receiving and holding at least two spade connectors. However, the spade prong is retained under spring force acting in linear contact against the prongs, thereby creating a zone of concentrated stress which can limit the life of both the terminal and the connector when the connection is frequently made and unmade. Surface wear can cause both a loosened mechanical connection and a poor electrical connection when protective conductive coatings are abraded.
A pair of tabs forming the base of the terminal disclosed in U.S. Pat. No. 3,910,671 are spoon-shaped or concave in configuration to provide four points of contact when inserted in a hole in a printed circuit board. This configuration precludes clinching, and especially precludes automated mechanical clinching, of the terminal tabs to the board. An unclinched, friction-held terminal is susceptible to displacement during successive component insertion operations conventionally carried out prior to soldering and the use of such terminals introduces serious quality control problems into the manufacturing process.